An exposure apparatus, utilized in the fabrication of semiconductor devices, liquid crystal display devices, and the like, has a stage apparatus to move an original plate, such as a mask or a reticle, or an exposed substrate, such as a semiconductor wafer or a glass substrate.
In this stage apparatus, generally, a laser interferometer and a reflecting mirror are used for stage position measurement.
Japanese Patent Application Laid-Open No. 2002-319541 discloses an apparatus having plural laser interferometers for stage position measurement. The position measurement is performed by selectively using the plural laser interferometers.
On the other hand, in the laser interferometer, a laser wavelength changes due to slight variations of air pressure, temperature and humidity, and causes a measurement error. Accordingly, the exposure apparatus is placed in a chamber for environmental control. At the same time, regarding the remaining variations, the wavelength is corrected with measurement values from an air pressure gauge, a temperature gauge, a humidity indicator, and the like.
When the position measurement is performed by selectively using plural laser interferometers, it is necessary to prevent occurrence of displacement before and after changing of an interferometer. For this purpose, it is necessary to provide overlapping sections where plural laser interferometers are able to measure and to inherit a prior measurement value before changing of the interferometer.
The wavelength correction described above is performed with an optical path length of a laser interferometer, the base point being determined upon being reset. In a stage apparatus in which the interferometer is not changed, wavelength correction is performed after the start of the apparatus, unless the apparatus is stopped due to an error, or the like. However, in a case wherein the interferometer is changed or interrupted, i.e., when a laser interferometer, which was light-shielded and disabled and has been brought online, the laser interferometer is reset each time. In the above case, as an XYZ position varies, the optical path length as a base point of the wavelength correction also varies. Without consideration of the amount of variation, a measurement error causes a displacement.